1. Field of the Invention
The present invention relates to a color cathode ray tube, and more particularly, to a shadow mask in a color cathode ray tube that can prevent formation of wrinkles on the shadow mask effectively occurred after welding.
2. Background of the Related Art
A related art color cathode ray tube will be explained with reference to FIGS. 1 and 2.
The related art color cathode ray tube is provided with a panel 1 having a fluorescent film 9 coated on an inside surface thereof, a funnel 3 having conductive carbon coated on an inside surface thereof, both of which are welded together with fusion glass. There is an electron gun 5 in one end of the funnel 3, for emitting electron beams, and a deflection yoke 7 on a neck portion of the funnel 3 for deflecting the electron beams. There is a shadow mask 30 fitted to a frame 13 for selecting colors to make the fluorescent film 9 on the inside surface of the panel 1 luminant. The frame 13 is fitted to stud pins 19 on the panel 1 by using springs 17. There is an inner shield 21, a magnetism shielding body, fitted to a rear of the frame 13 for preventing the electron beams from deviating off an original path by an influence of an external geomagnetism. The color cathode ray tube has a danger of implosion owing to a high vacuum inside of the color cathode ray tube. For preventing this, the panel 1 is designed to have a structural strength to withstand the atmospheric pressure. A reinforcing band 23 is strapped around a skirt of the panel 1 for dispersing a stress on the cathode ray tube of high vacuum for enhancing an impact resistance.
An assembly of the shadow mask and the frame will be explained in detail with reference to FIGS. 3xcx9c6.
The shadow mask 30 is provided with an effective surface part 32 having a plurality of electron beam pass through holes, i.e., slots 38, formed therein for passing the electron beams from the electron gun 5 to make the fluorescent film 9 ruminant, and an edge part 34 having no slots 38 formed thereon for reinforcing a strength of the effective surface part 32. The edge part 34 is welded to the frame 13, to assemble the shadow mask 30 to the frame 13.
In the meantime, the shadow mask 30 is designed to prevent the shadow mask 30 from being vibrated, i.e., to prevent howling. That is, a tension is applied to the shadow mask 30 in up and down directions (when the cathode ray tube is seen in front thereof), for increasing a natural frequency of the shadow mask 30, thereby preventing the howling, which will be explained in detail. As shown in FIG. 3, a compressive load xe2x80x98Pxe2x80x99 is applied to the frame 13 of an appropriate rigidity at first. Then, as shown in FIG. 4, in a state the compressive load xe2x80x98Pxe2x80x99 is applied to the frame 13, the shadow mask 30 is placed on the frame 13 and welded by using a welding roller 40, and the compressive load to the frame 13 is removed, to allow the frame 13 to restore an original position by an elastic force, thereby making a state in which the tension is applied to the shadow mask 30.
The operation of the related art color cathode ray tube will be explained briefly.
When a video signal is received at the electron gun 5, thermal electrons are emitted from the electron gun 5, and travel toward the panel 1 while the thermal electrons are accelerated and focused by acceleration electrodes and focusing electrodes in the electron gun 5. In this instance, a path of the electron beams are adjusted by the deflection yoke 7 for directing onto the inside surface of the panel 1. The electron beams directed toward the panel is involved in color selection as the electron beams pass through the slots 38 in the shadow mask 30, and the selected electron beams hit onto the fluorescent film 9 on the inside surface of the panel 1, to make the fluorescent film ruminant, that reproduces a video signal.
Currently, a high precision, and light weighted cathode ray tube is required, which may be attained by reducing a pitch Ph of the shadow mask 30 or making a thickness of the shadow mask 30 thinner. However, the reduced pitch Ph of, or thinner shadow mask 30 causes another problem in that it is difficult to avoid formation of wrinkles owing to deformation of the shadow mask 30 after welding, because stress concentration around a welding point 36 varies with the thickness xe2x80x98txe2x80x99 and the horizontal pitch Ph of the shadow mask 30. That is, as shown in FIG. 6, when the compressive force xe2x80x98Pxe2x80x99 is removed after welding the shadow mask 30, the tension is applied to the shadow mask 30 to concentrate the stress around the welding point 36. The stress in the vicinity of the welding point 36 is higher than an average stress "sgr"n, and becomes the higher as it goes nearer to the welding point "sgr"3 greater than "sgr"2 greater than "sgr"1, until a maximum stress exceeds a yielding stress, when a plastic deformation occurs, to form the wrinkles.
Therefore, for attaining a high precision and light weighted cathode ray tube by providing finer pitches of the slots and thinner shadow mask, though an appropriate measure is required for preventing the stress concentration to a certain limit, suggestion of such a measure has not be an easy work to do.
Accordingly, the present invention is directed to a shadow mask in a color cathode ray tube that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a shadow mask in a color cathode ray tube, which can effectively prevent formation of wrinkles on the shadow mask after welding while a finer pitch of slots and a thinner shadow mask are provided.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the shadow mask in a color cathode ray tube includes an effective surface part having a plurality of slots formed therein for passing electron beams, and an edge part extended from the effective surface part and welded to a frame fitted to a panel in a cathode ray tube, wherein an interval of welding spots on the edge part is fixed according to a thickness of the shadow mask and a pitch of slots of the shadow mask.
The interval of the welding spots is preferably in a range 11-19 times of the thickness of the shadow mask. And, the interval of the welding spots is preferably in a range 0.5-1.9 times of the slot pitch of the shadow mask.
The welding spot on the edge part has preferably an aspect ratio in a range of 1.0-2.6. And, the welding spot on the edge part has preferably a height in a range of 0.6 mm-0.9 mm, and a width in a range of 1.0 mm-1.4 mm.
Thus, the present invention permits to set up an optimal form of the welding spot that causes to form no wrinkles regardless of the thickness and the pitch, thereby preventing defective shadow mask coming from occurrence of wrinkles effectively, to improve productivity and to save cost by reduction of defects.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.